1. Field of the Invention
The present invention relates to a printer apparatus which prints an image in a recording material such as a recording sheet based on image information.
2. Related Background Art
Conventionally, printer apparatuses which are used for an output device of a computer or the output device for digital images can be divided into a thermal transfer type printer apparatus, an ink jet printer apparatus, a laser printer apparatus, a dot-wire printer apparatus and the like according to the recording methods. In the conventional printer apparatuses, line thermal transfer type printer apparatus is one in which an ink sheet and the recording sheet are used, plural heat generating elements arrayed in a main scanning direction are selectively driven while the ink sheet and the recording sheet are conveyed in a sub-scanning direction, and thereby the dot line-shaped image printing can be performed onto the recording sheet. Recently, a thermal transfer type printer apparatus comes to widespread attention with progress of input devices such as a digital camera, a digital camcorder, and a scanner which deal with the image. The thermal transfer type printer apparatus is suitable for the printer apparatus for performing print output of electronic image information taken by a still camera or a camcorder, which records a still picture, through a computer or a storage medium.
In the printer apparatuses adopting other printing methods such as the ink jet printer apparatus, because only binary selection whether a dot is formed or not exists, apparent resolution and gradation are obtained by techniques such as an error diffusion method while the small dots are formed on the recording sheet. On the other hand, in the thermal transfer type printer apparatus, because a controllable heat level can easily be changed in one pixel, a number of gray scale levels can be secured for one pixel. Therefore, the thermal transfer type printer apparatus has an advantage that smooth image can be obtained with high quality when compared with other printer apparatuses such as the ink jet printer apparatus. Further, in the thermal transfer type printer apparatus, performance of a thermal head which is of recording means and performance of a recording sheet material are also improved, so that an image print which is not pale against a silver-salt print in finished quality. Therefore, in particular the thermal transfer type printer apparatus receives attention for the printer which outputs a natural image as it keeps pace with the recent progress of the digital camera.
A system, in which a print of the image information is directly output without directly connecting the thermal transfer type printer apparatus and the image pickup devices such as the digital camera and the digital camcorder or without processing the image information by the devices such as the computer, already comes on the market. According to such systems, a photographic print of the image information from the digital camera and the digital camcorder can easily be output, so that the thermal transfer type printer apparatus further comes to attention. However, in the thermal transfer type printer apparatus, it is necessary that the transfer is performed by repeatedly superposing plural color kinds of ink in order to perform full color printing. A general configuration for realizing the full color printing will be described below.
FIGS. 9A and 9B schematically show a first example of a configuration of the conventional thermal transfer type printer. As shown in FIG. 9A, for the printing, a recording sheet P is wound around a platen roller 300 whose outer periphery is slightly longer than a total length of the recording sheet P, an ink sheet 302 and the recording sheet P are pressed by a thermal head 301 and the platen roller 300, ink on the ink sheet 302 is thermally transferred to the recording sheet P by heat generation of the thermal head 301 while the platen roller 300 is rotated. As shown in FIG. 9B, in order to perform the next color printing after the first color printing is completed, the press of the thermal head 301 is released, and the platen roller 300 is rotated to feed the recording sheet P to a printing start position. Then, the second color and subsequent other colors are printed by the same action as for the first color.
FIGS. 10A and 10B are schematic views showing a second example of the general configuration of the conventional thermal transfer type printer. As shown in FIG. 10A, for the printing, the ink sheet 302 and the recording sheet P are pressed by the thermal head 301 and a platen roller 303, and the recording sheet P is conveyed by a pair of a capstan roller 304 and a pinch roller 305, which is provided on the downstream side in a printing direction, while the ink on the ink sheet 302 is thermally transferred to the recording sheet P by the heat generation of the thermal head 301. As shown in FIG. 10B, in order to perform the next color printing after the first color printing is completed, the press of the thermal head 301 is released, and the recording sheet P is returned to the printing start position by rotating the pair of the capstan roller 304 and the pinch roller 305 and a pair of a return roller 306 and a pinch roller 307 in an opposite direction to the printing direction. Then, the second color and subsequent other colors are printed by the same action as for the first color.
The above two conventional methods are in common use. In the first example, since it is necessary to use the platen roller whose outer periphery is slightly longer than the total length of the recording sheet, the apparatus is enlarged. Further, a mechanism (not shown) which holds the recording sheet while the recording sheet is wound around the platen roller is also required, so that the first example has a demerit that the apparatus becomes complicated. However, when the first color printing is ended, since the printing start position of the second color exists immediately after the first color, a time for returning the recording sheet is not required unlike the second example. Therefore, the first example has a merit that high-speed printing is achieved.
On the other hand, the second example has the merit that both miniaturization and simplification are easy to realize in the apparatus while having the demerit that a printing time becomes longer.
While it is desirable that the photographic print of the image information from the digital camera and the digital camcorder is easily output, like a frameless photograph, a need to perform the printing to the whole surface of the recording sheet is increasing.
In the conventional first example, Japanese Patent Application Laid-Open No. 2003-39760 discloses the configuration in which the printing is performed to the whole surface of the recording sheet with no margin. However, in the configuration disclosed in Japanese Patent Application Laid-Open No. 2003-39760, the mechanism which winds the recording sheet around the platen roller is further complicated. Accordingly, the problems of the upsizing and the complication, which the conventional first example potentially owns, become further pronounced.
In the conventional second example, since the platen roller has no rotating mechanism, a leading end of the recording sheet can be conveyed only from a state in which the leading end is sandwiched between the capstan roller and the pinch roller, which generates a range where the printing cannot be performed to an upper end portion of the recording sheet. The range corresponds to a distance from the thermal head to the roller (shown by X in FIG. 10B).
In the configuration of the second example, the platen roller can be rotated. However, because hardness and a nip width of the platen roller are set so as to satisfy printing conditions caused by pressures and contact statuses between the thermal head and the ink sheet and between the ink sheet and the recording sheet, it is difficult to set the hardness and the nip width of the platen roller to the same level as for the capstan roller which has recording-sheet conveying accuracy necessary for the full color printing. On the contrary, when the hardness and the nip width of the platen roller are set to the same level as for the capstan roller which has the recording-sheet conveying accuracy necessary for the full color printing, there is a considerably high possibility that the printing conditions are not satisfied.
In the configuration close to the second example, Japanese Patent No. 2531358 discloses the configuration in which the printing is performed to the whole surface of the recording sheet with no margin. The configuration has the feature in that the belt is extended with a tension with a tension so as to involve the platen roller to convey the recording sheet. However, when the platen roller is driven while the belt is extended with a tension with a tension so as to involve the platen roller with a small winding angle like Japanese Patent No. 2531358, a slip is easy to occur between the platen roller and the inside surface of the belt, which directly worsens the recording-sheet conveying accuracy to impair the print quality. Further, as described above, since the settings of the hardness and the nip width of the platen roller are determined from the printing conditions, the settings cannot be performed while the higher priority is given to the conveying accuracy of the belt. Accordingly, the configuration disclosed in Japanese Patent No. 2531358, in which the belt and the recording sheet are conveyed using the printing platen roller as a main drive source, becomes a potential factor which impairs the print quality. Therefore, although the print quality can be permitted in the monochrome direct thermal printer in which ribbon is not used, the high-quality image similar to the photographic level cannot substantially be achieved when the configuration disclosed in Japanese Patent No. 2531358 is adopted to the full color printer.